The investigators propose to study the mechanism of AZT resistance and suppression of AZT resistance by suppressor mutations. They well also study RT mutations that alter catalytic activity, non-nucleoside RT inhibitors, and various nucleotide analogues. They propose to characterize quantitatively the formation of conformationally active stable complex formed between HIV-1 RT, primer-template, and deoxyribonucleoside triphosphate (dNTP) when phosphodiester bond synthesis is prevented. They well monitor the formational changes that occur in the formation of stable complex by measuring nuclease protection, dissociation rate in absence of dNTP, circular dichroism spectral changes, and changes in intrinsic protein fluorescence. In addition, they will study the effects of these mutations on RNase H endonuclease and exonuclease activity. Finally, they well characterize a novel AZTTP-dependent DNA modifying activity of HIV-1 RT that they recently identified. The unifying hypothesis is that drug-resistance mutations render the enzyme less effective at DNA chain termination.